Be careful how you use GPS

pnichols wrote:
The "errors" in the GPS system probably result primarily from the accuracy of the maps used, the interpretation of those maps, and the keeping-current of those maps as used by the GPS system ... more so than accuracy variations in the GPS system's determinaton of where the user is located.

It's very complex what the GPS system is intended to provide, and I can only imagine the work required to make it, and keep it, accurate. It is what it is at any given time and location, so as is usual with so many tools - it's user beware.

I once was using a GPS mapping system that provided the ability to adjust the "Snap To" distance. The maps are always improving but the vehicle sticks to the road even if the actual position is calculated to be beside the road. The displayed position snaps to the road. By tinkering with this value I could be driving close to many roads.

There is a road in Newfoundland that the vehicle position is yards from the displayed road. It is the map that is off and the actual position is beyond the Snap To setting or design limit of the software. It will be on my list next trip to check again to see if the map has been moved to the actual road position.

MrWizard wrote:
GPS device picks up three different satellites, and triangulate your position coordinates, then gets the map info that matches that data
Please explain how magnetic shift changes the orbital position of those satellites
Also for cellular devices, how would magnetic shift change the position of the cell towers

It has to do with direction. When you are in a parking lot and set a point in Google Maps, you have to start moving to have the map arrow point in the right direction. If you have two GPS receivers that talk to each other, one can derive the direction to which you are pointing (heading) while maintaining a fixed position. When on water patrols on the boat using GPS and marine charting software, the arrow just spins around when you stop in one spot in a one Receiver system. On a ship, dynamic positioning relies on multiple GPS receivers.

Try this with your iPhone. Turn off in Privacy the setting for System Services / Compass Calibration. Go into Google Maps and let the Cell Tower triangulation put you on the map. Now turn around in one spot. In my I7, Google Maps does not show which direction I am facing. Go back to Privacy /Location Services / System Services and enable Compass Calibration. Now Google Maps shows me the direction to which i am pointing the iPhone and turns when I do. The compass has assisted the cell triangulation to determine direction. I don't have access to other cell brands.

When one is moving on land or water, the GPS receiver is updating on some built in frequency, like 2 seconds or less frequent. My BadElf receiver is settable for how often I want it to update the triangulation calculation. This governs how frequent the map position is updated and how much detail goes into curves.

Cell service is not available everywhere which is why I use a separate GPS receiver with maps and charts that are resident on the iPhone or iPad. I don't have builtin GPS in the vehicles. The chart plotter in the boat just slowly and randomly spins when completely stopped as it loses the ability the calculate a pointing direction for a fixed position with only one receiver and is not integrated into a compass.

So, a GPS system can operate without a compass. A compass can give you a heading but not position without lots of calculations of multiple directions. A phone with GPS receiver and/or cell triangulation plus compass can give you all sorts of info. A GPS derived position and compass heading can get you out of the woods with no cell service.
Anything that takes down cell service leaves you dependent on a GPS receiver and map plotting. Is a compass and a magnetic point on the earth a system of last resort to find your way out of the wrong turn if the satellites are quiet ?
And of course all of the above could be hooey.

toedtoes wrote:


And in the case of the OP, it wasn't that the GPS was taking people incorrectly, it was that the people were too naive/dumb/impatient enough to realize that in a flood situation, GPS is not going to differentiate between a flooded road and a non-flooded road.

Snow, not flood. But, I agree with you.

Well, the article states:

Fortunately, as Beggan told Reuters, the errors only affected navigation in the Arctic and northern Canada. People using smartphones in New York, Beijing, or London, for example, would not have noticed the north magnetic pole's recent shifts.


So I guess unless you are RVing in the arctic or northern Canada, you don't have much to worry about.

I should have added this. Three years ago Dad's last Cousin on his Mom's side passed.
I did not remember the name or address of the Funeral home but figured I would find it once on the road which I did remember.I just entered the road, in the built in GPS in the AMG.
I got off the interstate turned right and in a bit the GPS arriving at destination 100 ft on the right.I was gobsmacked. No funeral home nor address entered but it took me to my destination. It was off by about 50 ft though.
No one believes me. It is probably till in the favorites in the GPS however, as I ahven't erased anything.

Hmmmmm ... I guess I fail to see how that satellites above the Earth that know where you are latitude-wise and longitude-wise according to a map base stored in it's GPS system computers ... can't precisely identify to you on your screen where you are latitude-wise and longitude-wise based on a matching map stored in your device??

That is UNLESS ... those two map bases don't match each other all the time! ;)

How does the Earth's magnetic field have anything to do with mis-matched map databases or pure software/geometry errors within the above process??

OR, does a shifting magnetic field slowly but surely over time change the positions of the GPS system satellites? :h

I don't shut down my ad blocker for any website, especially one that says I have to in order to read their stuff. Thanks, but no thanks.

Thanks for the info on how GPS receivers work.

Here is a link that might confuse you.

https://www.businessinsider.com/earths-magnetic-north-pole-moved-navigation-2019-2

That's it exactly. Which is why GPS is more accurate in urban areas than in undeveloped areas. Because maps of urban areas are very well made and the roads are not apt to change. With undeveloped areas, they may try to use forest service maps and such which show dirt trails, old unused logging roads, and such. These are the directions that GPS gets wrong.

And in the case of the OP, it wasn't that the GPS was taking people incorrectly, it was that the people were too naive/dumb/impatient enough to realize that in a flood situation, GPS is not going to differentiate between a flooded road and a non-flooded road.

The "errors" in the GPS system probably result primarily from the accuracy of the maps used, the interpretation of those maps, and the keeping-current of those maps as used by the GPS system ... more so than accuracy variations in the GPS system's determinaton of where the user is located.

It's very complex what the GPS system is intended to provide, and I can only imagine the work required to make it, and keep it, accurate. It is what it is at any given time and location, so as is usual with so many tools - it's user beware.